ECU for a 7afe in a 5sfe 1996 manual celica Options

[thebestofall007]

Hello all, I found a surprise in my 1996 Celica: It has an ECU for a 7afe manual transmission engine, however, mine is a 5sfe manual. The engine runs well, but gas mileage is not as good as it is supposed to despite replacing the cap, rotor, plugs, wires, and I get a P0141 code despite replacing the O2 sensor with an OEM Denso and checking the wiring connection between the sensor and the computer. The cables don't appear to be all spliced up, either.

Why would someone do this, and what would I have to do to replace it with the original (if this would fix the gas mileage and sensor issues)?

This post has been edited by thebestofall007: Oct 21, 2016 - 5:00 PM

[VavAlephVav]

Yeah, I'm surprised it works I'd guess it has all the same signals it's just going to be sending the wrong amount of fuel n such. As to why they did it, obviously because that's just what they could find and it worked. If you had to buy one of those things from Toyota back in the day it would have cost you a **** load of money. You can buy refurbished ones on Rockauto.com for $250 or if you get lucky you might find one at a salvage yard. I'd check for part-out threads too.

[slavie]

If I were you, I'd check the pinouts of 5S and 7A ECUs to make sure they match before you plug in a 5S ECU. Whomever did this in the first place might have re-pinned the ECU connectors to match the 7A ECU pinout, and if you don't pin it back you may have further issues.

Of, you may try to get the 7A O2 sensor, until you find the correct ECU at least.

The ECU really doesn't do as much "engine control" if you boil it down - it's just injectors and ignition, really. Most of the other crap is emissions, various sensors, AC, and so on. Given how conservatively Toyota ECUs are tuned, it's not too much of a surprise that it does run. Really cool nonetheless.

Yeah, I'm surprised it works I'd guess it has all the same signals it's just going to be sending the wrong amount of fuel n such. As to why they did it, obviously because that's just what they could find and it worked. If you had to buy one of those things from Toyota back in the day it would have cost you a **** load of money. You can buy refurbished ones on Rockauto.com for $250 or if you get lucky you might find one at a salvage yard. I'd check for part-out threads too.

Not necessarily - 5SFE would have bigger injectors to match it's increased displacement, so the amount of fuel may actually be correct, or close enough that the ECU may correct it with fuel trims - LTFT can add or subtract up to 20% before triggering CEL

This post has been edited by slavie: Oct 22, 2016 - 7:48 PM

[thebestofall007]

If I were you, I'd check the pinouts of 5S and 7A ECUs to make sure they match before you plug in a 5S ECU. Whomever did this in the first place might have re-pinned the ECU connectors to match the 7A ECU pinout, and if you don't pin it back you may have further issues.

I found some pinout PDFs from shop manuals that might help in this:

5SFE

7AFE

I also want to get the plugs off the donor's wiring harness when I go to the wrecking yard to get the ECU to compare to mine so I can see if the previous owner did re-pin my plugs and re-pin them back if necessary.

This post has been edited by thebestofall007: Oct 26, 2016 - 8:52 AM